This invention relates to testers for industrial pipe and other tubular goods and more specifically relates to such testers which apply hydrostatic pressures to the pipe under test.
As used herein the term "pipe" relates to tubular goods including drill pipe, casing production pipe, and other industrial tubulars utilized to transfer fluids from one location to another location. The term "water" as used herein is understood to include any non-compressible fluid suitable for implementing the hydrostatic testing of pipe described herein.
The need for testing both new and used pipe hydrostatically has been recognized, and various systems have been proposed in an attempt to satisfy the need. The need is especially apparent in the oil industry wherein several thousand feet of such pipe traditionally is run into the borehole and encounters tremendous loading conditions. Improper testing can fail to detect troubles which appear in such harsh usage.
Several thousand feet of pipe run into a borehole creates tremendous tensile loading conditions on the pipe. Some prior art testers have employed compressive forces on the pipe to retain the test head on the ends of the pipe during testing. These do not place a tensile loading onto the pipe while under internal pressure. Testing the pipe in this manner will not provide the harsh tensile loading condition to which it will be subjected in the well. Rather, such a compressive columnar load may create residual stresses in the pipe which could create future problems with axial loading.
Some users may prefer a means of testing pipe that does not stress the threads during testing. Others may prefer to have the pipe in an axial stress condition caused by the test. Further, many users prefer that the hydro test not put any stress on the threads with the thought that the test "plug" changes the mechanical characteristics of the thread. However, the structure of the machine using essentially the same structure allows a simplified conversion from a threaded test arrangement to a nonthreaded test assembly.
There are other improper tests which also can directly cause future troubles when placed into such a harsh environment as a borehole. For example, a common way to hydrostatically test a pipe is to employ a threaded test head screwed onto the threads on the end of the pipe under test. First, a cross threaded connection can damage the threads. Second, if insufficient torque to the threaded connection is initially applied, leakage can occur during testing. The application of additional torque while under pressure may likewise damage the threads. Such damaged threads can eventually leak or strip to cause failure of the coupling in the borehole due to the tremendous forces imposed on the pipe in the borehole.
Further, test heads become worn and may have poorly fitted or non-gaged threads which can cause thread distortion. The thread is deformed by coining or cold forging to cause a very low strength connection. Even though the pipe under test will accept a mating thread in later application, it is unlikely to have the integrity of a properly gaged nonstressed thread. It thus is likely to fail in later application.
Another important aspect of hydrostatically testing pipe is safety. Hydraulic pressures as high as 15,000 pounds per square inch may be required during hydrostatic testing. If the threaded test head is not adequately anchored to the pipe under test, the test head may blow off at very high hydraulic pressures; i.e. especially likely when threads become worn or crossed. Since the test heads may weigh up to 100 lbs, and since such a test head blowing off the pipe under test may be hurled at a velocity of several hundred feet per minute due to the high pressure, there is an extreme hazard both to the testing equipment and to human safety.
Many prior art testers have required bulky, extremely heavy support structures due to the high pressure requirement. Such prior art structures not only have been prohibitively expensive for many applications, they have been unsuitable for portable application, such as field usage.
Accordingly, the need remains for a suitable hydrostatic pipe tester of a lightweight design which allows portability yet which provides adequate testing conditions and assurances of safety to the operator.